The Zellidja Lead Smelter Company (Eastern Morocco) was created by Jean Walter in 1939 for the purpose of transforming lead concentrates into pure metal. Its activity was always at the origin of the production of huge quantities of solid mining waste with granular aspect. Today, despite the definitive cessation of its production in 2012 due to the depletion of ore, millions of tons of slag are piled up between the back of the foundry and the watercourse of Oued El Heimer. This open-air storage site represents a significant environmental and economic risk resulting from the surface water and groundwater pollution. In addition, as part of the strengthening of the Moroccan construction sector and infrastructure (which requires enormous quantities of natural aggregates), studying the possibilities of using these by-products as building materials seems interesting. For these reasons, the objective of our research work is the characterization of Zellidja slag for their valorization in civil engineering. This valorization has three objectives: to solve the problem of the landfill of the mining waste, to search for an alternative material responding to the increased needs for granular materials and to protect the national patrimony in raw material. In order to ensure the feasibility of this valorization, these tailings were the subject of a complete characterization. The results of this characterization prove that these by-products with a granular aspect have interesting geometric, physical, chemical and mechanical characteristics favoring their valorization in concrete.